Very slow water meter movement no leak to be found

[Unregistered]

Hi All

I am hoping you can give me a bit of advice. I recently noticed my stop tap is very tight, so I tested the tap out in the road. All ok and stopped water supply. However I noticed the 0.0001 dial was moving every so slowly when tap was back on, I guess many would have missed it. I have managed to turn the stopcock off (with a spanner) to isolate the under slab pipe, no movement on the meter so that brings me to internal leaks. I have done all of the following and still the 0.0001 dial moves ever so slowly:-

Changed tap valves in leaking kitchen taps
Changed flush and filler valve in old school toilet as the old one drop fed the cistern after the main refill
Isolated cold water supply to Megaflo unvented cylinder to isolate whole hot water system
Turned off other appliances at isolator valves

I am at a loss of where this "leak" is it is a little movement on the meter normal? On monitoring it moves say 600ml to 1 litre overnight.

Any advice is much appreciated.